1. Field of the Invention
The present invention relates to a flanging or curling device particularly for articles obtained by thermoforming from thermoformable sheet material.
2. Description of Related Art
Various arrangements for the flanging or curling of hollow objects such as beakers, cups, tubs or the like, all having a circular upper perimeter, trays and the like obtained by moulding by thermoforming from a thermoformable synthetic material, especially sheet material, have been proposed. See for example Italian Patent No. 85008 A/89 filed on the Dec. 18, 1989 in the name of O.M.V. Spa.
The arrangements proposed hitherto invariably provide for the supply of heat to the object to be curled before or during the flanging stage so that the edge of the article being flanged is suitably heated. This is because the flanging operation takes place after the hollow objects have been thermoformed and stacked. Of course in order to be transferred to a flanging machine the objects have to be first transferred to a separating or unstacking station arranged to separate the objects from each other and deliver them in sequence to a feeder for the flanging machine. Feeders with preheated rollers threaded with a variable pitch for progressive separation of the objects are widely used in the art.
Belt or suction tube feeding devices which are however, like roller feeders, only used for flanging round objects have also been proposed.
The flanging device in turn substantially comprises a generally fixed seat to receive an object to be curled and a die which is designed to mate with the inner edge of the receiving seat engaged by the partly curled edge of the object which is to be flanged.
With the high levels of productivity which can be achieved with the most up-to-date and sophisticated thermoforming units with mask conveyors, see Patent Application No. VR92A000012 filed on the Mar. 2, 1992 in the name of O.M.V. Spa, or other known systems, a conventional flanging device is not capable of keeping up with production line work where polypropylene or polyethylene, or the like are used.